Oscillators



R. ADLER OSCILLATORS Aug. 7, 1956 Hls ATTORNEY.

Modulcnn Signal Sourse oscnmnroas Robert Adler, Northfield, El.,assigner to Zenith Radio Corporatioiu a corporation of illinoisApplication August 10, 1953, Serial No. 373,255 4 Claims. (Cl. Z50- 36)This invention pertains to new and improved oscillators suitable for useat relatively high frequencies and more particularly to oscillatorsemploying beam-deflection tubes and to the structure of beam-deflectiontubes adapted for use in high-frequency oscillators.

Relatively recent advances in the electronics art have brought about anincreased use of the higher-frequency portions of the frequency spectrumfor commercial purposes, as exemplied by the very-high-frequency (V. H.F.) and ultra-high-frequency (U. H. F.) television broadcast bands andthe frequency-modulation radio band. As a result, manufacturers ofreceivers adapted for use at these frequencies have been faced with thenecessity of developing suitable stable oscillators for generating,demodulating or heterodyning signals within the same general range offrequencies. intensity-modulation devices of the familiar grid-controltype which are capable of operation as oscillators within both the V. H.F. and U. H. F. ranges have been developed; however, these tubes presentseveral inherent difficulties, among which are the necessity formaintaining relatively exacting dimensional tolerances in the electrodestructures of the tubes and the problems presented in compensating forchanges in the electrical characteristics of the devices due tovariations in thermal operating conditions. Velocitymodulation devicessuch as klystrons and magnetrons, on the other hand, appear to be toocomplex and expensive for most receiver applications and are notparticularly satisfactory for operation in the lower or V. H. F. portionof the newly-utilized frequency ranges.

ln addition to the intensityand velocity-modulation devices noted above,high-frequency oscillators employing beam-deection tubes have beenproposed. Conventionally, a beam-deflection tube so employed comprisesan electron gun for projecting a stream of electrons along a referencepath, a pair of deflectors disposed on opposite sides of that path, anda pair of anodes arranged on opposite sides of the path and spaced fromthe deectors. Each anode is connected to the deflector on the oppositeside of the beam path from that anode, and a resonant circuit isconnected across the anodes. Oscillators of this type are operable overa relatively wide range of frequencies; however, they are inherentlylimited to frequencies at which the electron transit time required forthe beam electrons to traverse the distance between the detlectors andthe anodes is substantially less than onefourth cycle or 90 at theoscillation frequency. Thus, construction of a beam-deilectionoscillator of this type for operation at V. H. and U. H. F. frequenciesbecomes quite inconvenient; small deflector-anode spacing which must beemployed in tubes adapted to operate at reasonable electrode voltagesmakes it diiiicult to obtain suicient transconductance.

Accordingly, it is a primary object of the invention to provide a newand improved oscillator for use at very-high or ultra-high frequencieswhich does not present the problems and diiiculties noted above inconnection with conventional devices.

Patented Aug.. '7, i956 lt is a further object of the invention toprovide a new and improved beamdeection tube which is capable ofsatisfactory operation as an oscillator within the V. H. F. and U. H. F.frequency ranges.

It is an additional object of the invention to provide a new andimproved oscillator utilizing a beam-deection tube which is relativelysimple and expedient to construct and economical to manufacture.

A beam-deflection oscillator constructed in accordance with theinvention comprises an electron gun for projecting a sheet-like beam ofelectrons along a reference path and a pair of anodes disposed onopposite sides of that path in spaced relation to the electron gun. Theoscillator further includes means for establishing a predeterminedvelocity for the electron beam comprising a pair of dellector electrodesdisposed on opposite sides of the reference path intermediate theelectron gun and the anodes, the centers of the deilectors being spacedfrom the anodes by a predetermined distance. A pair of conductiveconnector elements of negligible impedance at the desired operatingfrequency are included in the oscillator; each of these elementselectrically connects one of the deflector electrodes to that one of theanodes which is disposed on the same side of the reference path. Aninductive load interconnects the defiector electrodes to form therewitha resonant circuit having a resonance period substantially equal totwice the electron transit time of the electrons of the beam through thepredetermined distance separating the deflectors and the anodes.

The features of the invention which are believed to be novel are setforth with particularity in the appended claims. The organization andmanner of operation of the invention, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawing, in whichthe elements are identified by like numerals in each of the figures, andin which:

Figure l is a perspective view of the electrode system of anelectron-discharge device constructed in accordance with the invention;

Figure 2 is a schematic representation of an oscillator constructed inaccordance with the invention, comprising a cross-sectional View of anelectron-discharge device including the electrode system of Figure l,taken along line 2 2 therein; and

Figure 3 is a cross-sectional, partly schematic view of anotherembodiment of the invention.

As shown in the perspective View of Figure 1, the electrode system of abeam-deflection tube or electron-discharge device constructed inaccordance with one embodiment of the invention comprises an elongatedcathode 10, having an electron-emissive surface 11, and a focusingelectrode 12 including a slot 13 which is centrally located with respectto emissive surface lll. An accelerating electrode 14 is included in thedevice and has a central aperture or slot l5 aligned withfocusing-electrode slot 13.

Cathode l0 and electrodes 12 and 14 comprise an electron gun le forprojecting a sheet-like beam of electrons along a p redetermined path.The terminology sheetlike beam of electrons, as used throughout thisspecification and inthe appended claims, refers to an electron beamhaving one principal cross-sectional dimension which is very muchgreater than a second principal cross-sectional dimension; the term isnot restricted to any particular cross-sectional configuration. Thus, asheet-like beam may be of rectangular configuration in cross sectionwith a thickness very much smaller than its width, or may be ofgenerally ellipsoidal cross-sectional configuration, similarlyelongated, or may be of annular or ring-like contiguration with theradial thickness of the annulus very much smaller than thecircumference. Consequently, it will be understood that the particularstructure shown for elec- E2 tron gun 16 is purely illustrative and thatany suitable structure for projecting a sheet-like beam in accordancewith the denition given above may be employed without departing from theteaching of the invention.

A pair of defiector electrodes 17 and 18 are disposed adjacent oppositesides of slot and are positioned intermediate accelerator 11/1 and apair of anodes 19 and 20. A suppressor electrode 21 is positionedbetween anodes 19 and 2i) and is aligned with slots 13 and 15. Anode 20and deflector 13 are electrically connected by a conductive connectorelement 22; preferably, deilector 1S, connector 22, and anode 2.1i areformed from a single continuous sheet of conductive material. A similarconnector element 23 provides a direct electrical connection betweenanode 19 and deflector 17 (see Figure 2). Connectors 22 and 23 may be ofconsiderably reduced height as compared to electrodes 17-2il in order toreduce Athe effective capacity between the deiiector electrodes.Electrodes 12, 14 and 17--21 and connectors 22 and 23 may be formed fromany of the many known conductive materials suitable for use in evacuatedelectron-discharge devices.

The electrode system of Figure 1 is shown in cross section in Figure 2,in which the normal or reference path of electrons from cathode 10 toanodes 19 and v20 is indicated by dash lines A. Cathode 10 is providedwith an indirect heater element 24 (not shown in Figure l) embedded ininsulating material 25 and supported within lthe cathode sleeve. Theentire electrode system is mounted within a suitable envelope 26,preferably a conventional miniature tube envelope, which is subsequentlyevacuated and gettered in any manner known in the art.

In the oscillator circuit illustrated in Figure 2, cathode 10 isconnected to a source of reference potential, here indicated as ground,and focusing electrode 12 is also connected to ground. The groundingconnection for the focusing electrode may be made within envelope 26 asillustrated or, if preferred, externally thereto. Accelerating electrode14 is connected to a source of positive unidirectional bias potentialBz-land suppressor 21 is connected to ground.

An inductive load comprising a coil 27 is connected across deilectorelectrodes 17 and 18 and may be provided with a variable tuningcapacitor 2 8. The load circuit comprising inductor 27 `and capacitor23,' in conjunction with the capacity between electrodes 17 and 1 8,forms a resonant circuit 29 having a predetermined resonance frequency,and, consequently, a predetermined resonance period. A source ofunidirectional positive potential Bi-lis connected to the electricalcenter ofimductor 27 to provide balanced bias potentials for anodes 19and 20 as well as defiectors 17`and 1S. Preferably, the voltagessupplied by sourcesBi-land Bz-lare of different values so thataccelerator. 1 4 and deectors 17 and 18 are maintained at different D.C. potentials. This difference in bias potential between the accelerator and the dellectors leads to the formation pfan electrostaticlens which may be employed `to, focus and direct the electron streammore accurately between electrodes 17 and 18. A sharply-focused electronbeam is highly desirable in that the effective transconductance ofdeflector system 17, 1S with respect to anodes 19, 2l) is directlydependent upon the width of the beam as it irnpinges upon the anodes'.In other words, 4the voltage difference between deflect'ors 17 and 1Snecessaryrtoldeect the beam from one anode to the other is directfunction of the width of the beam as it strikesthe anodes, so that thesensitivity of the device is materially increased by the use of a moreaccurately focused beam. l Use of more sharply focused beam also permitsthe utilization of a smaller seperation distance d between deflectorsV17and 1S. Preferably, Bi-lis of lower potentialthan Bz+ in order toprevent the return of secondary electrons from anodes 19 and 20 to theelectrodes of gun 16. It will be 4 understood, of course, thatindividual potential sources Bfr-{- and Bz-l-` may be replaced by asingle source of unidirectional positive potential having separate tapsfor different voltages and that coil 27 may be connected to anodes 19and 20 or connectors 22 and 23 if preferred.

When the oscillator illustrated in Figure 2 is placed in operation,space electrons originating at ernissive surface 11 of cathode 10 arefocused by passing through slot 13 of electrode 12 and are acceleratedas they traverse slot 1 5 in the electrode 14. The electron streamfollows ref-J erence path A and passes between detiector electrodes 17and 18, impinging upon anodes 19 and 20. Diversion of the total beamcurrent to the two anodes is provided by suppressor 21, which is atalower potential than the anodes. As in `any conventional beam-deiiectiontube, the mean path of the beam from the effective center of deflectiontoward anodes 19 and 2G may be controlled by varying the potentialdiiference between electrodes 17 and 18,., 1lf the potentials of thedeiiectors are equal, the beam divides substantially equally between:modes 19 and 20 androperation in this manner is indicated in thedrawing for purposes of convenience. However, it may be desirable undercertain circumstances to operate the beamdeflection tube under biasconditions in which there is a potential dilerence between dellectors 17and 18 so that the path of the electron beam is displaced from originajlpath A, and an arrangement of this type is entirely withinrthe scope ofthe present invention. It should be noted that electrodes 17 and 1S areestablished at a positive potential with respect to cathode 1e so thatthe electrons emitted from surface 11 traverse the deflection system ata predetermined velocity corresponding to that potential.

The centers of deiiection electrodes 17 and 18 are separated rom thecollecting-surface plane of anodes y19 and 20 by a predetermineddistance D. For operation as an oscillator, resonant circuit 29 is tunedto a frequency having a resonance period which is substantially equal totwice the electron transit time required for the electrons of the beamto traverse distance D. Expressed differently, the centers of deflectors17 and 18 are spaced from anodes 19 and 211 by the predetermineddistance D which corresponds to an electron transit angle, for thevelocity determined by the potential level ofthe dedectors, ofapproximately one-half cycle or 180 at the desired oscillationfrequency. Theoretically, oscillation could be sustained for any yelectron transit angle between toA 270" in practice, the transit anglemust be considerably clos'erto 'the ideal one-half cycle.

Consider now that deector electrode 18 is instantaneously positive withrespect to deiiector 17, so that t'h`e` electron stream is deflectedtoward anode 20, as indicatedby dash line A. The deflected beam impingesonly upon anode 20, which receives the full beam current; accordingly,anode 20 becomes negative with re- 4spect toy anode 19. This change inthe relative potentials off anodes 19 and 20 results in an immediatecorresponding change in the relative potentials of deilectors 17, 1 8,due to the direct conductive connections provid'edby connectors 22, 23between each of the anodes and the defiect'or positioned on the sameside of path A. To achieve this effect, of course, conductive connectors2 2, 23 must be of negligible impedance at the desired operatingfrequency of the oscillator. Consequently, d eetr 17 becomes positivewith respect to deflector 1 8 `and the sense o'f the beam deection is'reversed so that Vit strikes only anode 19. Anode 19 then becomesnegative with respect to anode 20 and the respective polaritie's ofdetiectors 17 and 18 are again reversed. Thus, each time that one of thedeflector electrodes goes positiven'with respect to the other deliector,the beam is deectediiiavdirection such that it causes a subsequent'rvsssl Ofjdeestion- However; as indicated above, a periodofvtinteapprtuimately equal to one-half the resonance period of circuitmesmo 29 is required for the electrons of the stream to traversedi-stance D between the center of deection and anodes 19, 20. As aresult, the sense of the beam deflection reverses twice during a timeinterval equal to the period of the resonant circuit and the alternationof the beam between anodes 19 and 20 establishes and sustains anoscillatory current in circuit 29.

The versatility and efiicienchy/ of the oscillator illustrated in Fig. 2may best be shown by means of a specific example, which is includedmerely by way of illustration and by no means as a limitation on theinventive concept. A beam-deflection tube has been constructed inaccordance with Figures l and 2 and employed as an oscillator operableover the U. H. F. frequency range. The deiiector length h (see Figure 2)was 0.135" and distance D was 0.160. The total height of electrodes 10,l2, 14 and 17-20 was nine-sixteenths inch. When incorporated in anoscillator essentially identical with that of Figure 2, the tubeprovided oscillation over a range from 340 to 1000 megacycles, despitethe fact that the reactance/resistance ratio or Q of circuit 29 was onlyapproximately 60. For l000megacycle oper-ation, the biasing potentialsemployed were 225 volts for anodes and defiectc-rs and 720 volts for theaccelerator. With 130 volts on deilectors and anodes and between two andthree miiiiamperes of beam current, oscillation was maintained over aband of frequencies ranging from 340 to approximately 700 megacycles, aratio slightly exceeding two to one. These particular gures for aspecific device and circuit demonstrate the wide high-frequency rangeover which the oscillator may be operated.

Figure 3 illustrates an oscillator which is in many respects identicalwith that of Figure 2; the structure of electron gun i6, deiiectors 17and 18 and connectors 22 and 23 is the-same as that of thepreviously-described embodiment. In the oscillator of Figure 3, however,anode 19 is extended so that it terminates approximately at the centerline of the electrode system, which corresponds to original beam path A.Anode 20, on the other hand, is terminated a very small distance frompath A, and an extension 30, which forms a part of anode 20, projectsacross the reference path behind anode 19. Resonant circuit 29 ismodified to include a parallel-wire inductive circuit-3l which isterminated by variable capacitor 2S. Separate leads 33 and 34 areprovided for anodes 19 and 20 respectively and are connected to biassource *Bi-{- through a pair of individual choke coils 35 and 36. Inaddition, a separate external lead 37 is provided for focusing electrode12.

As in the embodiment of Figure 2, the electrons following path A impingein substantially equal numbers upon anode 19 and extension 30 of anode20; accordingly, static conditions are the same as for the electrodesystem of Figures l and 2. As before, the beam velocity is adjusted sothat the electrons traverse distance D between the center of deflectionand anodes 19 and 20 in a time interval approximately corresponding toone-half cycle at the resonance frequency of circuit 29. Operation ofthe oscillator of Figure 3 is thus in all essential respects identicalwith that of Figure 2, so that a repetition of the operationaldescription of the device is deemed unnecessary.

For ordinary oscillator operation, lead 37 is grounded. However, if itis desired to amplitude-modulate the output signal of the oscillator,lead 37 may be connected to a modulating signal source 38 so that asuitable modulating signal may be applied to electrode 12. On the otherhand, if frequency-modulation of the oscillator signal is founddesirable, the modulating signal may be superimposed upon the anodebiasing potential B1-{. Because such a signal varies the potential ondeilectors i7 and i8, it modifies the velocity of the electron streamand therefore causes variations in the transit time of the electronstraversing distance D. The average operating frequency of the device isdetermined by the resonant frequency of circuit 29', `and the appliedsignal frequencymodulates the cutre-n tl in the oscillator circuit.

In order to obtain oscillation at relatively low beam current, deiiectorlength h should be considerably larger than the space d between thedeflectors. A high aspect ratio (lz/d) limits the amplitude of theoscillatory current to a rather low level, since the electron beam isintercepted by the trailing ends of electrodes 17 and 18 whenever thevoltage between the deflector electrodes exceeds a predetermined level.This low-level amplitudelimiting characteristic is highly desirable formany local oscillator applications; a lower aspect ratio permitshigher-amplitude oscillation current but also requires more beam currentto sustain oscillation. For eifective operation, defiector length hshould not greatly exceed the distance traversed by the electron beamduring a time interval equal to one-half the resonance period of circuit29.

Althou-gh the circuitry of the oscillators of the invention is extremelysimple, they provide oscillation over a wide range of frequencies muchhigher than those obtainable in conventional beam-deiiection oscillatorsusing comparable voltages and electrode dimensions. In addition, if amore compact oscillator is desired, the inductive load represented bycoil 27 may be formed as part of the electrode system and includedwithin envelope 26. It should be noted that accelerator 14 may beomitted from gun i6, in which case the leading edges of defiectors lliand i8 serve as accelerators for the electron beam; however, theillustrated construction is preferred where a high deilector-anodetransconductance is desired. The electrode structures of thebeam-deflection tubes are extremely simple in configuration and theelectrodes are relatively few in number; all of the electrodes may bemanufactured from thin metallic sheets by punching or similarinexpensive mass-production techniques. The spacing between the variouselectrodes is not particularly critical from a manufacturing standpointand permits the utilization of reasonable dimensional tolerances. Inaddition, and for the same reasons, variations in the spacing betweenelectrodes which may result from changes in thermal operating conditionsdo not adversely affect the stability of the oscillator.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may he made without departing from theinvention in its broader aspects. Accordingly, the aim in the appendedclaims is to cover all such changes and modifications as may fall withinthe true spirit and scope of the invention.

I claim:

l. A beam-deflection oscillator adapted for operation over apredetermined range of frequencies, said oscillator comprising: anelectron gun for projecting a sheetlike beam of electrons alo-ng areference path; a pair of anodes disposed on opposite sides of saidreference path in spaced relation to said electron gun; means forestablishing a predetermined velocity for said beam cornprising a pairof deflector electrodes disposed on opposite sides of said referencepath intermediate said electron gun and said anodes, the centers of saiddeflectors being spaced from said anodes by a predetermined distance; apair of conductive connector elements of negligible impedance over saidpredetermined range of operating frequencies, each of said elementselectrically connecting one of said deilector electrodes to that one ofsaid anodes disposed on the same side of said reference path as said onedetlector electrode; and an inductive load interconnecting saiddefiector electrodes to form therewith a resonant circuit having aresonance frequency within said range and a resonance periodsubstantially 7 equal to tvvice the electron transitptime of theelectrons of said beam through said predetermined distance.

2. A beam-'deflection Oscillator adapted for operation' over apredetermined range of frequencies, said oscillator comprising: Y anevacuated envelope; an electron gun mounted within said envelope forprojecting a sheet-like beam of electrons along a reference path; a`pair of anodes disposed within said envelope on 'opposite sides of saidreference path in spaced relation to said electron gun; a suppressorelectrode disposed within said envelope between said anodes; means forestablishing a predetermined velocity for said beam comprising a pair ofdeflector electrodes disposed within said envelope on opposite sides ofsaid reference path intermediate said electron gun and said anodes, thecenters of said deectors being spaced from said anodes by apredetermined distance; a pair of conductive connector elements ofnegligible impedance over said predetermined range of operatingfrequencies disposed within said envelope, each of said elementselectrically connecting one of said deflector electrodes to that one ofsaid anodes disposed on the same side of said reference path as said onedeector electifode; and an inductive load interconnecting said defleetorelectrodes to form therewith a resonant circuit having a resonancefrequency within said range and a resonance period substantially equalto twice the electron transit time of the electrons of said beam throughsaid predetermined distance.

3. A beam-dellection electron-discharge device for generating electricaloscillations of a given frequency comprising: an electron gun forprojecting a sheet-like beam of electrons along a reference path; a pairof anodes disposed on opposite sides of said reference path in spacedrelation to said electron gun; means for establishing a predeterminedvelocity for said beam comprising a pair ofpdeector electrodes disposedon opposite sides of said reference path intermediate said electron gunand said anodes, the centers of said deectors being spaced from saidanodes by a predetermined distance corresponding to an' electron transitangle at said predetermined velocity of approximately one-half cycle atsaid oscillation frequency; and a pair of conductive connector elementsof negligible impedance at said oscillation frequency, ea'ch of saidelements electrically connecting one ot said dellector electrodes tovthat one of said anodes disposed on the same side of said reference pathas said one dellector electrode.

4` A beam-deect'ion electron-discharge device for generating electricaloscillations of a given frequency comprising: an electron gun forprojecting a sheet-like beamy of electrons along ya reference path; apair of anodes disposed on opposite sides of said reference path inspaced relation to said electron gun; means for establishing apredetermined velocity for said beam comprising a pair of detlectorelectrodes disposed on opposite sides of said reierence pathintermediate said electron gun and said'anodes, the centers of saiddeectors being spaced from said anodes by a predetermined distancecorresponding to an electron transit angle at said predeterminedvelocit'y of approximately one-half cycle at said oscillation frequency;and a pair of connector elements of negligible impedance at saidoscillation frequency, each of said elements electrically connecting onei of said defiector electrodes to that one of said anodes disposed onthe same side of said reference path as said one deliecto'r electrode,each said connector element with its associated anode and detlectorelectrode being formed from a single continuous sheet of conductivematerial.

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